Near Polichnitos, at an altitude of 60 meters, on the banks of the Almyropotamos, the hot springs of Polichnitos spring up. These springs are characterized as the hottest springs in Europe, as the temperature of the water at the gushing points reaches 87.6°C. The high temperatures can be justified as the temperature of the water in the subsoil, at this point, reaches 400°C.
The gushing of the springs is due to geological faults that appear in the area. Through the fragmented rocks along the fault it is facilitated the penetration of water deep into the crust. There it meets the still hot magmatic chambers of the volcanoes of Lesvos that were active for 16 million years, as a result of which it is heated and enriched in minerals and gases. The gases then increase the pressure, and help it return through the fault surfaces to the surface and erupt as hot springs.
All the hot springs of Polichnitos are chlorinated. In relation to sea water, the sodium chloride of the hot springs is three times less. But it is believed that there is some mixing of this water with sea water up to about 30%.
The intense yellowish and red colors that appear in the rocks in the area of the eruption are due to the precipitation of iron oxides, such as limonite and hematite.
